The present invention relates to an apparatus and a method for hanging apparatus on the inner diameter of a downhole tubular, such as an existing casing string in a wellbore. In one of its aspects, the invention relates to an improved liner and a method of hanging a liner from an existing casing section or other tubular in a wellbore.
In the field of wellbore operations, liners are strings of pipe, used to case open holes below an existing casing. It is known to use liner hangers to anchor a liner to the inner diameter of an existing casing string. A number of techniques have been employed to meet these aims.
It is often necessary to anchor apparatus and tools other than liners in downhole tubulars, for example to cover up holes in casing. Examples include the hanging or anchoring of packers, plugs, bridge plugs, sandscreens, scab liners or other apparatus.
Generally, existing hanging methods are unsuitable for tight tolerance or close clearance casing schemes. The tolerance of standard casing is not tight enough to allow for substantial surface variations on a tubular or tool being hung, such as surface irregularities, without risk of the tubular or tool jamming within the casing.
PCT Application Number PCT/GB03/01895 describes a method and apparatus for expanding tubulars. This involves radially expanding a first smaller diameter tubular into frictional contact with a second larger diameter tubular or well bore. The disadvantage of this method is that an expanding helical band, such as therein described, is weakened as it is expanded and will part if put under too much pressure. Additionally radial deformation of the first tubular will lead to a decrease in the tensile strength of the first tubular.
U.S. Pat. No. 6,223,823 describes a method of installing a casing section in a well, where in one aspect a technique known in the art as dimpling is used. Here, discrete sections of the liner profile are forced to expand into corresponding eccentric undercuts of the existing casing in order to fix the casing being installed in the required position. This is achieved by means of forcing a number of pellets or dimple formers radially outwards into the liner.
A disadvantage of this technique is that dimpling alone is insufficient to sustain a high hanging load and slippage often occurs. Furthermore this technique requires an eccentric undercut being formed on the existing casing. This is another distinct disadvantage as it is difficult to make such undercuts inside a casing when already in place. Therefore, such formations must be carried out well in advance, or a compatible casing must have been installed when the bore was cased.
It is an object of at least one embodiment of the present invention to provide apparatus for anchoring to an existing casing string that obviates and mitigates one or more disadvantages and limitations of the prior art.
Moreover, it is an object of at least one embodiment of the present invention to provide a means for hanging apparatus in an existing casing string that is integral to the wall thickness of the apparatus.
It is a further aim and object of at least one embodiment of the invention to provide a method and apparatus for suspending, anchoring or hanging apparatus from the inner diameter of an existing downhole tubular in a wellbore which obviates or mitigates the disadvantages and drawbacks associated with the prior art.